Envelopes normally have a front side carrying the address or an address window, to which is connected at one side a closing flap, and on the other side a bottom flap or rear side, which is bonded to the side flaps, around which is folded the front side.
Several systems exist for closing or sealing an envelope following the filling thereof.
A gumming of the closing flap makes possible to close the same after moistening. However, this closure is unreliable, because the holding force is dependent on the degree of moistening and the adhesive also requires a certain time for hardening, so that if the envelope is excessively filled the flap easily springs open again before the glue has set.
There are also self-adhesive envelopes with a latex adhesive, which is applied both to a fold-back flap located on the rear side and to the closing flap. Normally this adhesive does not adhere to other surfaces, but only to the adhesive coating corresponding thereto, so that closure takes place by pressing together the two like latex adhesive coatings. However, this cohesive adhesive suffers from the disadvantage that it does not provide a very reliable closure and can optionally be opened in non-destructive manner. It more particularly has an ageing tendency, so that such so-called self-adhesive envelopes, particularly under the influence of heat, completely lose their closing force after a short time.
In addition, contact adhesive envelopes are conventionally used, in which a relatively aggressively adhering contact adhesive is applied to the closing flap. Its adhesive force is very great, the closure is reliable and closing can easily take place. However, it suffers from the disadvantage that prior to use the contact adhesive must be covered by a separate, siliconized cover strip, which must be pulled off for use purposes. It must then be disposed of, which is disadvantageous. It is known from DE 43 14 685 A to apply the contact adhesive to the cover strip and then stick the latter to the closing flap.
WO 90/11 943 discloses an envelope with an adhesive closure, where a contact adhesive is applied to the fold-back flap. Part of the envelope back associated therewith is coated with a parting agent. Thus, in the unused state the fold-back flap is flapped against the parting agent coating. After filling the envelope the fold-back flap is unfolded and can now be bonded to the closing flap. The disadvantage arises that the contact adhesive coating can only cover part of the fold-back flap, because otherwise it would not be possible to mechanically fold the latter and this impairs the reliability of closure.
The problem of the invention is to provide an envelope, which also includes dispatch bags, packs, etc., as well as a method and device for producing the same, which for closure purposes permit the use of a very effective, ageing-resistant adhesive without residual products (e.g. cover strips) and without any disadvantages concerning the shape and serviceability of the envelope.
This problem is solved by the envelope according to claim 1.
Through the application of the contact adhesive to the parting coating and the folding over the same of the envelope part on which the contact adhesive is to be finally provided, the contact adhesive on folding said area again is transferred to the envelope part not coated with a parting agent and is ready for use. The adhesion of the adhesive coating to the part not coated with the parting agent (fold-back flap) is much greater than on the parting agent coating. This avoids any application of contact adhesive to an area which, following its application, must be folded round. This facilitates manufacture, because e.g. a folding roller need only have a corresponding recess at the point facing the area coated with contact adhesive, whereas the up to then uncoated fold-back flap can be gripped at a random point and folded round. It is also possible to substantially completely provide the fold-back flap with contact adhesive and in particular up to the lateral edges in order to increase the reliability of closure. This is aided by the fact that the contact adhesive normally requires no drying. Up to now envelopes required holding-down devices on a drying section and gaps had to be left in the gluing for the same.
In an embodiment of the invention contact adhesive is only provided for the fold-back flap. The back of the envelope has a parting coating in the area on which the fold-back flap rests in the flapped back state. Thus, the adhesive surface of the contact adhesive is covered by the envelope back with the parting area provided thereon. This is not prejudicial either during transportation or during filling. After flapping up the fold-back flap it is free and can be bonded to the closing flap free from adhesive.
In another embodiment the contact adhesive can be provided on the closing flap and the parting coating covering the same in the unused state on the inside of the envelope, namely in an area which is exposed by the folded round fold-back flap. After folding up the fold-back flap it is bonded with the contact adhesive to the closing flap.
The contact adhesives used can be of a conventional nature, e.g. synthetic resin dispersions having a water base and with adhesive characteristics with respect to the envelope material used. Use can also be made of hotmelts, which are applied at processing temperatures of e.g. 120 to 200xc2x0 C., but which have a permanent adhesive action even at ambient temperature. A strong adhesive action is evolved without requiring moistening or any other activation prior to bonding. One water-based product which can be used is commercially available under the trade name xe2x80x9cEukalin 5354 Haxe2x80x9d, and a hotmelt with the trade name xe2x80x9cSwift H 686/4xe2x80x9d. The parting agent coating, which is either applied as a separate coating or which can already be present on the material used, can e.g. contain an acrylate resin, silicone acrylate or some other silicone compound. The dehesive property is important. Use can be made of any release varnishes or lacquers, whose properties are based on the fact of closing the pores and therefore providing no touching possibility for the contact adhesive.
As the contact adhesive requires no drying prior to the further processing of the envelope, during the manufacture of the latter there is no need for a drying section taking up a large part of the manufacturing machine. In order to permit the application of the normal moisture-activatable gumming and so as to keep the drying section short, it was hitherto necessary to have a very significant staggering or overlapping of the envelopes in the machine. This can now be reduced or can be completely obviated in certain circumstances.
If the contact adhesive is applied to the parting agent coating, this occurs before the fold-back flap is folded back. For folding back a folding station is needed, which is constructed in such a way that the envelope does not get caught on the corresponding folding tools as a result of its contact adhesive coating. As a result of a corresponding recess on a folding roller provided in the folding station and/or a parting agent coating at this point this feature can be fulfilled.
These and further features can be gathered from the claims, description and drawings and the individual features, both singly or in the form of subcombinations, can be implemented in an embodiment of the invention and in other fields and can represent advantageous, independently protectable constructions for which protection is claimed here.
The subdivision of the application into individual sections and the subheadings in no way limit the general validity of the statements made thereunder.